1. Field of the Invention
This invention is directed toward an improved tree harvesting head. The invention is more particularly directed toward an improved tree harvesting head of the type that can be rotated about an axis that is perpendicular to the longitudinal axis of the head.
The invention is also directed toward a method of harvesting employing a harvesting machine with the tree harvesting head of the present invention.
2. Description of the Prior Art
Tree harvesting heads having a central post with a circular saw at the bottom, the plane of the saw transverse to the axis of the post, tree grapple means above the saw head on the post and tree accumulator means on the post above the grapple means, are known. The head has a bracket on the back of the post and a pivot pin mounts the head, via the bracket, on the end of a boom carried by a mobile vehicle. The axis of the pivot mounting is horizontal, the pin extending transverse to the boom and allowing the head to be tilted from an upright, vertical position to a generally horizontal position while generally aligned with the boom. This allows the operator to place accumulated cut trees, held by the head, on the ground. Usually the boom must be rotated, and/or the vehicle moved, to place the trees in the desired position on the ground. This is energy inefficient, however, given the weight of the boom and/or the vehicle.
It is known to mount the head on the boom with both the above tilt mounting and a rotatable mounting allowing the head to be rotated out of alignment with the boom. The rotatable mounting is located between the bracket and the head. Such a mounting allows the trees to be placed in the desired position on the ground by rotating the head about the rotatable mounting. Since the head is lighter than the boom or the vehicle, this arrangement is much more energy efficient. Examples of such heads are shown in U.S. Pat. Nos. 4,552,191 and 5,441,090 by way of example. These known heads, however, are quite poorly designed, particularly with regard to the type and size of the rotatable mounting employed and to the drive means for rotating the head. The rotatable mounting is quite small in diameter and thus subject to early failure. The drive means also employ large rotatable members on the head adding to its weight and making it less efficient.